Extended instrument run times between battery charges are highly desirable in many gas detector applications. As the power consumption of a typical 4-gas instrument is dominated by the flammable gas detecting channel, this power consumption and battery life can be important issues.
Both accepted methods for flammable detection (catalytic and optical) traditionally suffer from high power consumption. And, as such, current battery capacities or their form factors may be unacceptable limitations for some gas detecting operations.
Developments in areas such as micro-hotplate substrates have driven down pellistor powers from ˜200 mW to ˜20 mW, but further major reductions are unlikely without unacceptable impacts on response time of the device. Bulb-based optical systems give the greatest in-band power levels, with resulting advantages for detection performance. Such systems have fallen from powers of ˜250 to ˜50 mW, but are believed to be unable to be reduced significantly further.
Most microelectromechanical systems (MEMs) thermal sources do not offer a particularly favorable power/speed combination. Attention has, therefore, turned to a new generation of light emitting diode (LED) sources in the 3 microns to 5 microns region. These devices can operate at much faster frequencies and output powers that approach or exceed the in-band optical outputs of bulb-based optical systems but with average power consumptions in the mW region or below.
Further, the trend toward smaller, slimmer portable instruments demands lower sensor profiles rather than the more traditional cylindrical industry standard 4-series types. The accompanying restrictions on available optical path-length place greater emphasis on the stability and performance of the detection systems. Therefore, the ability to provide a reference which reduces the impact of non-gas effects on the sensor output is of growing importance.